[76.07] On the X-ray Spectral Evolution of Nova Cygni 1992 in the First Two Years After Outburst

Nova V1974 Cygni 1992 has been accepted as a prototype of classical nova
owing to its unique data set in almost all wavelengths.
We present a further analysis of the archival X-ray data obtained by
ROSAT PSPC on several pointings from 1992 April 22 to 1993 December 3.
The soft X-ray emission arising from the H-burning
white dwarf envelope (between 0.1-0.7 keV energy range) is fit with a new
nova blackbody emission model that accounts for the absorption of
X-ray photons by enhanced abundances in the
white dwarf atmosphere (MacDonald 1994, private communication).
A complete evolution of the white dwarf
on a Hertzsprung-Russell diagram is presented using two different
atmosphere models of NeO and CO rich compositions.
The soft X-ray flux derived using the new NeO blackbody
model is in the range (1.7-2.3)\times 10^-7 erg\ s^-1\ cm^-2 during
the constant bolometric luminosity phase. The peak photospheric temperature
\sim 51 eV (5.9 \times 10^5 K) is reached at about day 500 with a photospheric
radius of (0.96-1.4)\times 10^9 cm for a 2-3 kpc source distance.
In addition, we present the spectral development of the hard X-ray emission
above 0.7 keV thought to originate from shocks within the nova wind.
The hard X-ray emission
evolves independently from the soft component reaching a maximum
\sim 150 days after the outburst with a peak
unabsorbed flux \sim 1.8 \times 10^-11\ erg\ s^-1\ cm^-2.
The total hard X-ray energy dissipated in the ejecta
is about 0.01 % of the initial explosion energy.